Compressed air operated apparatus for raising underwater deposits

ABSTRACT

Apparatus for raising deposits, using a pressure medium, the material being raised being conveyed via a dredge pipe from the deposit to a separator in which the material raised is separated from the pressure medium and possibly from entrained portions of a liquid medium disposed above the deposit, the pressure medium being introduced at the lower end of the dredge pipe into the latter with a rotational component and in such a manner that a partial vacuum is produced under the effect of which the material to be raised enters the dredge pipe, the inlet end of the dredge pipe being held during dredging at a small distance from the deposit.

United States Patent 51 3,673,716

Trondle July 4, 1972 54] COMPRESSED AIR OPERATED 1,327,651 1/1920 Beaven ..37 72 ux APPARATUS FOR RAISING 1,530,654 3/1925 Daley ....37/63 x UNDERWATER O IT 2,599,980 6/1952 Dunning... .....37/62 S S 2,711,598 6/1955 Craggs, Jr ..37/62 [72] Inventor: Alois Trundle, Wasserburger Landstrasse 3,148,464 9/1964 Jones .....37/67 209, 8000 Munich 82, Germany 3,253,357 5/1966 Al1ard.... ..37/65 3,301,606 1/1967 Bruno .....37/61 UX [221 Sept-2211969 3,359,741 12/1967 Nelson .....37/72 ux [21] I Appl. No.: 859,872 3,474,549 10/1969 Schnell 37/61 FOREIGN PATENTS OR APPLICATIONS 30 F'Al't'P"tDta 1 pp y a 416,730 12/1946 Italy ..37/61 Dec. 20, 1968 Germany ..P 18 16 221.5 591,481 4/1959 Italy ..299/9 851,333 10/1960 Great Britain ..37/72 [52] 11.8. C1 ..37/61, 37/67, 302/58,

417/ 197 Primary Examiner-Robert E. Pulfrey [51] Int. Cl. ..E02f 3/92 Assistant Examiner-Clifford D. Crowder [58] Field of Search 37/61-67, 72; Att0meyCraig, Antonelli & Hill [57] ABSTRACT [56] Reierences Cited Apparatus for raising deposits, using a pressure medium, the UNITED STATES PATENTS material being raised being conveyed via a dredge pipe from the deposit to a separator in which the material raised is separated from the pressure medium and possibly from entrained portions of a liquid medium disposed above the deposit, the pressure medium being introduced at the lower end of the dredge pipe into the latter with a rotational component and in such a manner that a partial vacuum is produced under the effect of which the material to be raised enters the dredge pipe, the inlet end of the dredge pipe being held during dredging at a small distance from the deposit.

PATENTEnJuL' 4 1912 3,673,716

SHEET it Of 4 COMPRESSED AIR OPERATED APPARATUS FOR RAISING UNDERWATER DEPOSITS This invention relates to a method of raising deposits, especially gravel and the like, using a pressure medium, especially by means of compressed air, the material to be raised being conveyed via a dredge pipe from the deposit to a separator in which the material raised is separated from the pressure medium and possibly from entrained portions of a liquid medium disposed above the deposit, the pressure medium being introduced at the lower end of the dredge pipe into the latter in such a manner that a partial vacuum is produced under the effect of which the material to be raised enters the dredge pipe. The invention further relates to an apparatus for carrying out this method.

Hitherto known methods and apparatuses of this type have the disadvantage that the output achieved in practice is generally small and irregular due to frequent blockages of the inlet opening and resulting interruptions in operation. It is also disadvantageous in many cases that in the known methods the material raised is segregated in that the suction effect acts predominantly on the coarser constituents and less on the finer constituents.

It is an object of this invention to provide a method and apparatus which obviate the aforementioned disadvantages.

This problem is solved by the method according to the invention in that the inlet end of the dredge pipe is held during dredging by tension means, such as cable winches or the like, closely against the inclined wall of the deposit.

The method according to the invention has the advantage that the material is removed not only from the base but also from the wall of the deposit, a cavity being formed in the wall by removal of material therefrom and material slipping down as a result. This method is particularly advantageous when raising gravel from water-filled gravel pits. Depending on the type of deposit, it may be advantageous firstly to arrange the axis of the lower dredge pipe end substantially perpendicular to the surface of the deposit by the tension means and secondly to hold the inlet opening of the dredge pipe at a predetermined substantially constant distance from the deposit, which is preferably substantially equal to l to l 5 times the diameter of the inlet opening of the dredge pipe. According to the invention, the loosening and removal of the material may be substantially promoted by cutting tools which preferably rotate concentrically to the inlet opening of the dredge pipe.

A very substantial improvement in the output and material removal results unexpectedly if the pressure medium is introduced according to the invention into the dredge pipe with a rotational component. The rotation of the pressure medium effects a turbulence in the region in front of the inlet opening of the dredge pipe which whirls up the deposit in this region. Surprisingly, it has been found that in this manner a segregation of the material raised is very effectively avoided and material in front and laterally of the inlet opening of the dredge pipe is also loosened. Conveniently, the pressure medium is made to rotate about the dredge pipe axis.

The pressure medium is advantageously supplied at the inlet end of the dredge pipe in the form of a flow which is of annular cross-section, moves along the inner surface of the dredge pipe and is substantially uniformly distributed over the periphery. lt may be advantageous to subdivide the pressure medium flow in the peripheral direction to obtain a more uniform bubble formation. The pressure medium may be guided in the injection nozzle by guide fins extending in the direction of flow to ensure a supply uniformly distributed over the periphery.

According to the invention, a floating free of the inlet opening of the dredge pipe may be effected in that pressure medium is conducted preferably intermittently against the conveying direction. For this purpose, the dredge pipe is connected preferably in the upper region of the conduits via a connecting conduit which may be shut off by means of a valve to the pressure medium conduit. Furthermore, a shut-off valve is provided in the dredge pipe above the opening of the connecting conduit and in the pressure medium conduit below the opening of the connecting conduit. Normally, the valve in the connecting conduit is closed whereas the valves in the dredge pipe and in the pressure medium conduit are normally open. If the pressure medium is to be diverted to the lower end of the dredge pipe, the valve in the connecting conduit is opened and the two other valves closed. 7

To carry out the method, according to the invention an apparatus may be used in which there is provided at the lower end of a dredge pipe a suction head at whose inlet end is introduced a pressure medium to produce a partial vacuum, said apparatus being characterized in that to introduce the pres sure medium an annular nonle provided with preferably helically wound fins imparting a rotational component to the compressed air is used.

According to the invention, it is particularly advantageous to make the inner edge of the inlet opening of the suction head piece substantially align with the inner wall of the dredge pipe. This construction aflords the advantage that undesirable turbulence at this-edge is avoided. According to the invention the dredge pipe may be surrounded by an outer pipe concentric with the axis thereof in such a manner that an annular space is left between the two pipes which is used as supply conduit for the pressure medium used for the dredging.

According to the invention the suction head may comprise an inclined roof which deflects material falling onto the suction head and facilitates withdrawal or freeing of the latter when buried under fallen material. The apparatus may be provided with cutting tools mounted rotatably concentrically with the dredge pipe axis and according to the invention to drive the cutting tools two or more hydraulic motors are used which are disposed symmetrically to the dredge pipe axis and distributed uniformly over the periphery and are preferably reversible in their directions of rotation. The symmetrical arrangement obviates asymmetrical loads and reduces the sealing and bearing problems. The drive and bearing of the cutting tools are preferably arranged in a substantially fluid-tight chamber which according to the invention is filled with a medium under pressure, thus reducing the danger of penetration of dirt, water or the like.

The chamber including the drive and bearings of the cutting tools may be connected to the supply conduit of the pressure medium used for the dredging, preferably by a controllable valve. The controllable valve is constructed as a non-retum or check valve so that it closes as soon as the excess pressure of the pressure medium in the supply conduit decreases. This valve arrangement assures that the pressure in the housing enclosing the motors is maintained even after the pressure in the supply conduit is decreased. It is also possible to ensure by a float control that when using compressed air as pressure medium the valve closes as soon as water enters the compressed air line. The supply conduits for the hydraulic fluid serving to drive the hydraulic motors are preferably arranged in the intermediate space between the dredge pipe and outer pipe, thus being protected against damage.

According to the invention, it is particularly advantageous for use in relatively great depths to provide the dredge pipe with resilient intermediate members. To take up the tensile stresses flexible support elements, preferably cables, may be provided. The resilient intermediate members prevent breakage or damage of the pipe in rough weather or by falling material. Moreover, they make it possible to incline the suction head or the lower portion of the pipe together with the suction head with respect to the rest of the pipe, so that the suction head may be brought more easily into the optimum working position. The suction head and the individual pipe sections may be secured to the flexible support elements, the resilient intermediate members thus being completely or partially free from tensile stresses.

According to the invention, the cutting tools may be so arranged that they partially cover the inlet opening of the suction head, thus preventing larger objects, such as stones, wood or the like, from becoming lodged in front of the inlet opening of the suction head and clogging the latter.

The cutting tools may be mounted on support ribs which extend with their one end substantially to the edge of the inlet opening of the suction head, a tooth-like cutting tool extending in each case from said end of the support ribs at about 30 to the dredgepipe axis downwardly towards the center of the suction head opening in such a manner that the distances between the free ends of said cutting tools are considerably smaller-than the internal diameter of the dredge pipe.

It is a further object of this invention to provide the lower end of the dredge pipe with a preferably frustro-conical air guide ringwhich extends into the innerannular space of the mouthpiece and to mount the mouthpiece of the suction head on the lower end of this support pipe, preferably by means of a thread, in axial displaceable manner such that the cross-sectionof the outlet opening of the annular nozzle is adjustable. The supply of pressure medium can thus be adapted to different operating conditions.

Some of the'objectsof this invention having been stated, other objects will appear as the description proceeds when taken in conjunction with the accompanying drawings, in which: I

FIG. 1 is a side.elevation of a section dredger carried by a floating raft and having a compressed air suction head in a water-filledgravel pit, 7

FIG. 2 is a longitudinal section through a suction head,

FIG. 3 is a perspective view of thelower end of the dredge pipe to an enlarged scale, and H FIG. v4 is a view of a modified embodiment of the pipe having resilient intermediate pipe members or sections.

FIG. 1 shows a floating suction dredger in a water-filled gravel pit. A suction head 1 is formed at the lower end of a double-walled pipe which is assembled-from pipe sections 3 Y and which issecured at its upper end so that it may be pivoted, raised and lowered on a raft or ship denoted generally by 2.

The sections 3 of the pipe each consist of an outer support pipe 10 and an inner conveying or dredge pipe 11. The pipe sections are joined together at the ends by means of flanges 12 so thatthey form a uniform double-walled pipe. The sections of the flanges .12 joining the outer support pipel to the inner dredge pipe 11 comprise openings 13 such that compressed air9 may be led downwardly between the outer support pipe 10 and the inner dredge pipe 11. At its lower end the suction head 1 comprises an annular mouthpiece 4 of substantially U- shaped cross-section, the inner wall 4' forming a slightly funnel-shaped inlet to the dredge pipe 11 having a cylindrical inner surface portion which comprises substantially the same internal diameter as the dredge pipe 11 in order to avoid any undesirable turbulence of the aspired mixture of material and water due to the free upper edge of the mouthpiece.

The upper end of theouter wall 4" of the mouthpiece 4 is screwed onto the lower end of the support pipe by means of a thread 5'.

The dredge pipe 11 carries at its lower end an air guide ring 7which widens conically downwardly and extends into the inner annular chamber of the mouthpiece 4, thus forming between the air guide ring 7 and the inner wall 4' of the mouthpiece 4 anannular nozzle 8 which tapers upwardly. The air guide ring 7 is provided at its inner side with curved and/or inclined air guide fins'6 which set the compressed air blown into the dredge pipe 11. into a rotational movement about the axis of thedredge pipe. The compressed air flowing out of the lower end of the annular chamber between the support pipe and the dredge pipe is led downwardly at the outside of the air guide ring, the outside of the air guide ring 7 likewise being providedwith air guide fins 6' which may also be curved and/or inclined to give the air an initial twist.

A two-part ring 15, is rotatably mounted on two roller bearings 14 and 14' mounted on the support pipe 10 so that a cuttingdevice provided with teeth 54 to 58 can rotate about the lower end of the support pipe 10 and the mouthpiece 4 connectedthereto.

The ring 15 is connected at its upper end face detachably to a flange :16 which isconnected in turn detachably to an internally toothed rim l7. Said toothed-rim 17 is set in rotary motion via pinions l8 and 19 by two or three hydraulic motors 20 and 21 serving to drive the cutting device and arranged symmetrically to the axis of the dredge pipe offset Ito I20cir cumferentially.

Hydraulic fluid conduits 22 and 23 leading to the hydraulic motors 20 and 21 are arranged in the intermediate space between the outer support pipe 10 and the inner dredge pipe 11 in which the compressed air 9 flows downwardly and extend through the openings 13. These hydraulic fluid conduits 22 and 23 are divided in sections which correspond in length to the length of the pipe sections 10 and which are detachably connected together substantially in the region of the flanges 12. Resilient intermediate members may be provided at the ends of the conduits 22 and 23.

The two hydraulic motors 20 and 21 are surrounded by a housing 24 which forms in its upper region an inclined roof. I

The lower end of the housing 24 is held in its position concentrically to the dredge pipe by a centering plate 33. The inclined roof 24 serves to facilitate extraction or freeing of the suction head when the latter is buried under falling material, such as grave] or the like.

The two hydraulic motors 20 and 21 are secured in a mounting plate 34 and the seat of each motor in the mounting plate must be sealed so that no water or dirt can penetrate into the inner chamber 26. Disposed in this inner chamber 26 are the two roller bearings 14 and 14 and the internal teeth of the internally toothed rim 17 as well as the two pinions 18 and 19. The inner chamber 26 is closed at its upper end by the mounting plate 34 fixedly connected to the outer support pipe 10.

Between the mounting plate 34 and an upwardly extending cylindrical extension of the toothed rim 17 is a radial sealing ring 28 which prevents water or dirt penetrating into theinner chamber 26. Furthermore, two slip sealing rings 29 and 30 are provided above this radial seal 28. At its lower end the inner chamber 26 is sealed beneath the roller bearings l4, 14 by a radial sealing ring 27. Inserted in the outer support pipe 10 is .a valve, preferably a check valve 31, by which compressed air may be introduced into the inner chamber 26 to produce an excess pressure preventing the entry of water, sand, dirt or the like and supporting the effect of the seals. An excess pressure may be produced in analogous manner'by means of a check valve 31 in the inside of the housing 24.

In its lower portion the suction head comprises cutting tools which consist of teeth 54 to 58 mounted on four support ribs 50 arranged offset by The support ribs are connected by means of screws 53 to the bearing ring 15and the flange 16. The support ribs 50 comprise in the upper region a portion 51 extending outwardly and in the lower region a portion 52 extending radially inwardly. A tooth 54 extends substantially radially from each support rib 50, two teeth 55 and 56 extend obliquely downwardly at an angle of about 60 to the suction head axis, one tooth 57 extends vertically downwardly and one tooth 58 is inwardly inclined at about 30 to 45 to the suction head axis. The teeth 58 mounted at the inner ends of the portions 52 are very effective in preventing larger stones, wood or the like becoming lodged in front of the inlet opening of the suction head and clogging said opening. The profile of the teeth 54 to 58 is shown in FIG. 2, in which the rear tooth 58 is indicated in dashed line.

During operation of the apparatus, the inlet opening of the suction pipe is advantageously about 20 cm above the material to be raised and is substantially perpendicular to thesurface thereof. By means of a cable 44 (FIG. 1) secured to the suction head 1 and wound on a winch 46 atthe end of the raft 2 adjacent the sloping wall of the gravel pit, the inlet end of the dredge pipe may be held closely against the sloping wall of the deposit. The outwardly extending teeth 54 to 56 can loosen material from the sloping wall of the deposit. The hydraulic motors 20 and 21 drive the cutting tools so that they rotate about the inlet opening. The teeth 54 to 58 thus loosen the deposit.

Compressed air is blown substantially in the conveying direction into the lower end of the dredge pipe 1 1 through the annular nozzle 8 at a pressure which is higher than the static pressure of the water obtaining in this depth. This produces a suction which aspires the material to be raised mixed with water and conveys it upwardly. The air guide fins 6 and 6' arranged in the nozzle 8 and externally on the air guide ring 7 impart to the compressed air a rotational movement about the axis of the dredge pipe before injection into the latter. This produces a swirling movement, the surprising effect of which is that the various constituents of the deposit, for example stones of various sizes and sand of various granulations, are raised unsegregated, i.e. in their natural mixture, which gives a uniform quality of the material raised. Moreover, an increase in output is obtained. The guide fins 6 obviously also result in a more uniform bubble formation of the compressed air emerging from the nozzle 8 and this may be one of the causes of the higher output.

From the upper outlet of the pipe the mixture of material, water and air is fed to a separator where the material is separated from the compressed air and the water. The material may then be conveyed via conveyor belts into ships or onto land.

When using the suction head in relatively great depths, in particular in depths over 25 m, the dredge pipe is preferably provided with resilient intermediate members which are inserted between the pipe sections 3 substantially at intervals of 12 to 15 m to avoid breakage of the pipe 3 in rough weather and on collapse of the material wall. FIG. 4 shows a resilient intermediate member 36 inserted directly above the suction head 1 and another intermediate member 36' inserted in the pipe further up. Two support cables 38 are provided to carry the suction head, the resilient intermediate members 36 and 36' thus being partially freed from the tensile stress. Fitted to the flanges of the resilient intermediate members are radially projecting eyes 42 through which the cables 38 are led.

These eyes 42 may be so designed that the cable is fixedly clamped therein. This latter construction of the eyes 42 affords the advantage that all the resilient intermediate members 36 and 36' are completely free from the tensile stress due to the weight of the pipe. Screws or wedges may be used to clamp the cable 38 in the eyes 42.

To produce the swirling or twist about the axis of the suction head of the compressed air blown into the dredge pipe it may be sufiicient to provide air guide fins only at the outside of the air guide ring 7 or alternatively only at the inside of said air guide ring. Instead of compressed air blown in through the annular nozzle 8 it is also possible to use another gas or a liquid, particularly water under pressure.

Instead of hydraulic motors, electric motors may be used.

It may also be advantageous to provide at the outer. periphery of the internally toothed ring 17 teeth directed radially outwardly which promote the loosening of the deposit at a steeply sloping wall.

Valves (not illustrated) are provided at the upper end of the pipe and make it possible to conduct the compressed air 9 through the dredge pipe 11 downwardly to float the inlet opening of the suction head 1 free or to remove blockages in the dredge pipe 11. These valves may be actuated in such a manner that the compressed air is led intermittently or in pulse manner through the dredge pipe.

In so far as they are novel compared with the prior art all the particulars and features contained in the documents and combinations thereof are claimed as essential to the invention.

In the drawings and in the specification there have been set forth preferred embodiments of the invention, and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being defined in the claims.

What is claimed is:

1. An apparatus operated by compressed air for raising deposits of gravel or the like from beneath bodies of water comprising a dredge pipe which is open at its extreme lower end and is immersible into water, a suction head attached to the lower portion of the dredge pipe, cutting tools surrounding said suction head and being rotatably attached thereto, motor means for driving said cutting tools, and an annular nozzle located at the lower end of said suction head for directing a supply of compressed air into the interior of the dredge pipe, wherein said annular nozzle is provided with inclined air guide fins, said dredge pipe being surrounded by a supporting pipe, the annular space between the two pipes serving as a conduit for the compressed air supplied to the annular nozzle, characterized in that each of both the supporting pipe and the dredge pipe include a plurality of sections, a respective section of the dredge pipe and respective section of the supporting pipe being connected to one another by common flanges at each end thereof, said flanges being connectable to the respective common flange of the adjacent supporting pipe and dredge pipe section, and said common flanges being provided with apertures for passage of the compressed air from the annular space of one section to the annular space of the adjacent section.

2. An apparatus according to claim 1, characterized in that the motor means comprises two hydraulic motors, said motors being supplied with hydraulic fluid through conduits arranged in said annular spaces.

3. An apparatus according to claim 1, wherein said annular nozzle includes an air guide ring attached to the end portion of the dredge pipe and an annular mouthpiece adjustably mounted for axial movement on the end portion of the supporting pipe, said air guide ring being shaped like the surface of the frustrum of a cone and widening in the downward direction to extend into said annular mouthpiece, whereby adjustment of said mouthpiece varies the opening of said annular nozzle.

4. An apparatus according to claim 3, characterized in that said guide fins are helically wound on the inner surface of said air guide ring.

5. An apparatus according to claim 4, characterized in that the outer surface of said air guide ring includes guide tins attached to the outer surface of said air guide ring.

6. An apparatus according to claim 3, characterized in that the upper portion of said air guide ring has a diameter corresponding to the diameter of said dredge pipe and in that said upper portion is rigidly and sealingly attached to the bottom of said dredge pipe to form a funnel inlet for the admission of compressed air into the dredge pipe end opening.

7. An apparatus according to claim 3, characterized in that said annular mouthpiece has an approximately U-shaped cross section with the open end extending upwardly for acceptance of said guide ring and the outer leg of the U being threadably attached to the supporting pipe.

8. An apparatus according to claim 7, characterized in that the surface of the inner leg disposed inside of and away from the U-shaped opening is arranged to provide a conically shaped opening tapering inwardly toward the dredge pipe end opening for admitting gravel of the like into the dredge pipe.

9. An apparatus according to claim 8, characterized in that some of said cutting tools are arranged below the bottom most portions of said mouthpiece.

10. An apparatus according to claim 9, characterized in that the radially innermost cutting tools are arranged radially inwardly with respect to the circumference of the inlet formed by the mouthpiece.

11. An apparatus according to claim 8, characterized in that the minimum diameter of said conically shaped opening is less than the inner diameter of the dredge pipe.

12. An apparatus according to claim 1, including means to intermittently force compressed air downwardly through the dredge pipe against the dredging direction for cleaning the lower opening.

13. An apparatus operated by compressed air for raising deposits of gravel or the like from beneath bodies of water comprising a dredge pipe which is open at its extreme lower end and is immersible into water, a suction head attached to the lower portion of the dredge pipe, cutting tools surrounding said suction head and being rotatably attached thereto, motor I means for driving said cutting tools, and an annular nozzle located at the lower end of said suction head for, directing a supply of compressed air into the interior of the dredge pipe, wherein said annular nozzle is provided with inclined air guide fins, said dredge pipe being surrounded by a supporting pipe, theannular space between the two pipes serving as a conduit for the compressed air supplied to the annular nozzle, characterized in that the motor means comprises two hydraulic motors, said motorsbeing supplied with hydraulic fluid through conduits arranged in said annular space.

l4..An apparatus according to claim 13, further comprising a housing annularly disposed about said support pipe and said motors, and sealing means to prevent water and debris from entering said housing.

- 15. An apparatus according to claim 14, characterized in that check valve means are included in the walls of the supporting pipe for the introduction of compressed air into said housing to assist the sealing means in precluding the entry of foreign materials into said housing.

16. An apparatus according to claim 13, including means to intermittently force compressed air downwardly through the dredge pipe against the dredging direction for cleaning the lower opening.

17. An apparatus as claimed'in claim 13, characterized in that said guide fins are helically wound on the surface of said annular nozzle.

l i t 

1. An apparatus operated by compressed air for raising deposits of gravel or the like from beneath bodies of water comprising a dredge pipe which is open at its extreme lower end and is immersible into water, a suction head attached to the lower portion of the dredge pipe, cutting tools surrounding said suction head and being rotatably attached thereto, motor means for driving said cutting tools, and an annular nozzle located at the lower end of said suction head for directing a supply of compressed air into the interior of the dredge pipe, wherein said annular nozzle is provided with inclined air guide fins, said dredge pipe being surrounded by a supporting pipe, the annular space between the two pipes serving as a conduit for the compressed air supplied to the annular nozzle, characterized in that each of both the supporting pipe and the dredge pipe include a plurality of sections, a respective section of the dredge pipe and respective section of the supporting pipe being connected to one aNother by common flanges at each end thereof, said flanges being connectable to the respective common flange of the adjacent supporting pipe and dredge pipe section, and said common flanges being provided with apertures for passage of the compressed air from the annular space of one section to the annular space of the adjacent section.
 2. An apparatus according to claim 1, characterized in that the motor means comprises two hydraulic motors, said motors being supplied with hydraulic fluid through conduits arranged in said annular spaces.
 3. An apparatus according to claim 1, wherein said annular nozzle includes an air guide ring attached to the end portion of the dredge pipe and an annular mouthpiece adjustably mounted for axial movement on the end portion of the supporting pipe, said air guide ring being shaped like the surface of the frustrum of a cone and widening in the downward direction to extend into said annular mouthpiece, whereby adjustment of said mouthpiece varies the opening of said annular nozzle.
 4. An apparatus according to claim 3, characterized in that said guide fins are helically wound on the inner surface of said air guide ring.
 5. An apparatus according to claim 4, characterized in that the outer surface of said air guide ring includes guide fins attached to the outer surface of said air guide ring.
 6. An apparatus according to claim 3, characterized in that the upper portion of said air guide ring has a diameter corresponding to the diameter of said dredge pipe and in that said upper portion is rigidly and sealingly attached to the bottom of said dredge pipe to form a funnel inlet for the admission of compressed air into the dredge pipe end opening.
 7. An apparatus according to claim 3, characterized in that said annular mouthpiece has an approximately U-shaped cross section with the open end extending upwardly for acceptance of said guide ring and the outer leg of the U being threadably attached to the supporting pipe.
 8. An apparatus according to claim 7, characterized in that the surface of the inner leg disposed inside of and away from the U-shaped opening is arranged to provide a conically shaped opening tapering inwardly toward the dredge pipe end opening for admitting gravel of the like into the dredge pipe.
 9. An apparatus according to claim 8, characterized in that some of said cutting tools are arranged below the bottom most portions of said mouthpiece.
 10. An apparatus according to claim 9, characterized in that the radially innermost cutting tools are arranged radially inwardly with respect to the circumference of the inlet formed by the mouthpiece.
 11. An apparatus according to claim 8, characterized in that the minimum diameter of said conically shaped opening is less than the inner diameter of the dredge pipe.
 12. An apparatus according to claim 1, including means to intermittently force compressed air downwardly through the dredge pipe against the dredging direction for cleaning the lower opening.
 13. An apparatus operated by compressed air for raising deposits of gravel or the like from beneath bodies of water comprising a dredge pipe which is open at its extreme lower end and is immersible into water, a suction head attached to the lower portion of the dredge pipe, cutting tools surrounding said suction head and being rotatably attached thereto, motor means for driving said cutting tools, and an annular nozzle located at the lower end of said suction head for directing a supply of compressed air into the interior of the dredge pipe, wherein said annular nozzle is provided with inclined air guide fins, said dredge pipe being surrounded by a supporting pipe, the annular space between the two pipes serving as a conduit for the compressed air supplied to the annular nozzle, characterized in that the motor means comprises two hydraulic motors, said motors being supplied with hydraulic fluid through conduits arranged in said annular space.
 14. An apparatus according to claim 13, further comprisinG a housing annularly disposed about said support pipe and said motors, and sealing means to prevent water and debris from entering said housing.
 15. An apparatus according to claim 14, characterized in that check valve means are included in the walls of the supporting pipe for the introduction of compressed air into said housing to assist the sealing means in precluding the entry of foreign materials into said housing.
 16. An apparatus according to claim 13, including means to intermittently force compressed air downwardly through the dredge pipe against the dredging direction for cleaning the lower opening.
 17. An apparatus as claimed in claim 13, characterized in that said guide fins are helically wound on the surface of said annular nozzle. 